.TH std::unordered_map::insert 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::unordered_map::insert \- std::unordered_map::insert

.SH Synopsis
   std::pair<iterator, bool> insert( const value_type& value );     \fB(1)\fP  \fI(since C++11)\fP
   std::pair<iterator, bool> insert( value_type&& value );          \fB(2)\fP  \fI(since C++17)\fP
   template< class P >                                              \fB(3)\fP  \fI(since C++11)\fP
   std::pair<iterator, bool> insert( P&& value );
   iterator insert( const_iterator hint, const value_type& value ); \fB(4)\fP  \fI(since C++11)\fP
   iterator insert( const_iterator hint, value_type&& value );      \fB(5)\fP  \fI(since C++17)\fP
   template< class P >                                              \fB(6)\fP  \fI(since C++11)\fP
   iterator insert( const_iterator hint, P&& value );
   template< class InputIt >                                        \fB(7)\fP  \fI(since C++11)\fP
   void insert( InputIt first, InputIt last );
   void insert( std::initializer_list<value_type> ilist );          \fB(8)\fP  \fI(since C++11)\fP
   insert_return_type insert( node_type&& nh );                     \fB(9)\fP  \fI(since C++17)\fP
   iterator insert( const_iterator hint, node_type&& nh );          \fB(10)\fP \fI(since C++17)\fP

   Inserts element(s) into the container, if the container doesn't already contain an
   element with an equivalent key.

   1-3) Inserts value.
   Overload \fB(3)\fP is equivalent to emplace(std::forward<P>(value)) and only participates
   in overload resolution if std::is_constructible<value_type, P&&>::value == true.
   4-6) Inserts value, using hint as a non-binding suggestion to where the search
   should start.
   Overload \fB(6)\fP is equivalent to emplace_hint(hint, std::forward<P>(value)) and only
   participates in overload resolution if std::is_constructible<value_type, P&&>::value
   == true.
   7) Inserts elements from range [first, last). If multiple elements in the range have
   keys that compare equivalent, it is unspecified which element is inserted (pending
   LWG2844).
   If [first, last) is not a valid range, or first and/or last are iterators into
   *this, the behavior is undefined.
   8) Inserts elements from initializer list ilist. If multiple elements in the range
   have keys that compare equivalent, it is unspecified which element is inserted
   (pending LWG2844).
   9) If nh is an empty node handle, does nothing. Otherwise, inserts the element owned
   by nh into the container , if the container doesn't already contain an element with
   a key equivalent to nh.key(). The behavior is undefined if nh is not empty and
   get_allocator() != nh.get_allocator().
   10) If nh is an empty node handle, does nothing and returns the end iterator.
   Otherwise, inserts the element owned by nh into the container, if the container
   doesn't already contain an element with a key equivalent to nh.key(), and returns
   the iterator pointing to the element with key equivalent to nh.key()(regardless of
   whether the insert succeeded or failed). If the insertion succeeds, nh is moved
   from, otherwise it retains ownership of the element. hint is used as a non-binding
   suggestion to where the search should start. The behavior is undefined if nh is not
   empty and get_allocator() != nh.get_allocator().

   If after the operation the new number of elements is greater than old
   max_load_factor() * bucket_count() a rehashing takes place.
   If rehashing occurs (due to the insertion), all iterators are invalidated. Otherwise
   (no rehashing), iterators are not invalidated.
   If the insertion is successful, pointers and references to the element obtained
   while it is held in the node handle are invalidated, and pointers and references
   obtained to that element before it was extracted become valid.
   \fI(since C++17)\fP

.SH Parameters

   hint        - iterator, used as a suggestion as to where to insert the content
   value       - element value to insert
   first, last - range of elements to insert
   ilist       - initializer list to insert the values from
   nh          - a compatible node handle
.SH Type requirements
   -
   InputIt must meet the requirements of LegacyInputIterator.

.SH Return value

   1-3) A pair consisting of an iterator to the inserted element (or to the element
   that prevented the insertion) and a bool value set to true if and only if the
   insertion took place.
   4-6) An iterator to the inserted element, or to the element that prevented the
   insertion.
   7,8) \fI(none)\fP
   9) An object of insert_return_type with the members initialized as follows:
     * If nh is empty, inserted is false, position is end(), and node is empty.
     * Otherwise if the insertion took place, inserted is true, position points to the
       inserted element, and node is empty.
     * If the insertion failed, inserted is false, node has the previous value of nh,
       and position points to an element with a key equivalent to nh.key().
   10) End iterator if nh was empty, iterator pointing to the inserted element if
   insertion took place, and iterator pointing to an element with a key equivalent to
   nh.key() if it failed.

.SH Exceptions

   1-6) If an exception is thrown for any reason, these functions have no effect
   (strong exception safety guarantee).
   7,8) No exception safety guarantee.
   9,10) If an exception is thrown for any reason, these functions have no effect
   (strong exception safety guarantee).

.SH Complexity

   1-6) Average case: O(1), worst case O(size()).
   7,8) Average case: O(N), where N is the number of elements to insert. Worst case:
   O(N * size() + N).
   9,10) Average case: O(1), worst case O(size()).

.SH Notes

   The hinted insert (4-6) does not return a boolean in order to be
   signature-compatible with positional insert on sequential containers, such as
   std::vector::insert. This makes it possible to create generic inserters such as
   std::inserter. One way to check success of a hinted insert is to compare size()
   before and after.

.SH Example


// Run this code

 #include <iostream>
 #include <string>
 #include <unordered_map>

 int main ()
 {
     std::unordered_map<int, std::string> dict = {{1, "one"}, {2, "two"}};
     dict.insert({3, "three"});
     dict.insert(std::make_pair(4, "four"));
     dict.insert({{4, "another four"}, {5, "five"}});

     const bool ok = dict.insert({1, "another one"}).second;
     std::cout << "inserting 1 => \\"another one\\" "
               << (ok ? "succeeded" : "failed") << '\\n';

     std::cout << "contents:\\n";
     for (auto& p : dict)
         std::cout << ' ' << p.first << " => " << p.second << '\\n';
 }

.SH Possible output:

 inserting 1 => "another one" failed
 contents:
  5 => five
  1 => one
  2 => two
  3 => three
  4 => four

   Defect reports

   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.

      DR    Applied to         Behavior as published              Correct behavior
                       overloads (3,6) would only            only participates if
   LWG 2005 C++11      participate in overload               value_type
                       resolution if P is implicitly         is constructible from P&&
                       convertible to value_type

.SH See also

   emplace          constructs element in-place
                    \fI(public member function)\fP
   emplace_hint     constructs elements in-place using a hint
                    \fI(public member function)\fP
   insert_or_assign inserts an element or assigns to the current element if the key
   \fI(C++17)\fP          already exists
                    \fI(public member function)\fP
   inserter         creates a std::insert_iterator of type inferred from the argument
                    \fI(function template)\fP
